System Traffic Estimation

The traffic estimation for the CDMA2000 system is directly dependant
upon the type and quality of services that will be offered and how they will
be transported. The traffic estimation process involves not only the radio
link, but also the other fixed facilities that comprise the network.

The process and methodology for conducting system traffic engineering,
that is, determining the amount of physical and logical resources that need
to be in place at different points and nodes within the network to support the
current and future traffic. The determination of existing traffic loads is
rather more straight forward in that you have existing information from
which to make decisions upon. For future forecasts, the level of uncertainty
grows exponentially the farther the forecast or planning takes you into the
future. However many elements in the network require long lead times,
ranging from three weeks to over one year to implement. Obviously, the goal
of traffic engineering is to design the network and its sub-components to not
only meet the design criteria, which should be driven by both technical,
marketing, and sales, but also be done so that it is achieved in a cost-effective
manner. It is not uncommon to have conflicting objectives within a design,
that is, to ensure that the customers have the highest QOS/GOS for both
voice and packet data, but yet have a limited amount of capital from which to
achieve this goal. Therefore it is important to define at the onset of the design
process, and have some interim decision points where the design process can
be reviewed and altered, if required, either by increasing the capital budget,
revisiting the forecast input, or altering the QOS/GOS expectations.
Because there will be different variants to circuit- and packets-switched
services offered, the variations will be vast. However, there are some commonalties
that can be drawn upon.

There are several methods that can be used for calculating the required
or estimated traffic for the network.
It is essential to note that there are several key points within the network
where the traffic engineering calculations need to be applied:

■ BTS-to-subscriber terminal
■ BTS to BSC
■ BSC-to-packet network
■ BSC-to-voice network

There are several situations and an unknown level of perturbations that
can occur in the estimation of traffic for a system. In an ideal world, the traffic
forecast would be projected by integrating the marketing plan with the
business plan, and coupled with the products that should be integral to both
the marketing and business plan. However, reality is much harsher, and usually
very little information is obtainable by the technical team from which to
dimension a network with.Therefore the following is meant to help steer the
new system planners in determining their traffic-transport forecast.
Initially, packet data traffic is expected to be low. The higher data speed
is a result of the data not being as time-sensitive as voice. Also, packet data
services are an enabler for more services offered by the operator.
The forecast would be much more simplified if the system were operational
because there would be real traffic information as well as a minimal
set of products from which to utilize. The forecast, or growth, could be
extrapolated from the business plan or simplified marketing plans, which
would specify a specific growth-level desired.
The equation to follow for an existing system would be
Total traffic
existing traffic  new traffic expected

The new traffic expected could be a simple multiplication of the existing
traffic load. For instance, if the traffic is 25 Mbps and the plan is to increase
the traffic by 25 percent over the next year, then the traffic forecast for the
one-year forecast would be altered by increasing the current traffic load at
each node by that amount and determining the requisite amount of logical
and physical elements needed in addition to any load sharing that might be
achievable.

If the traffic forecast is available only on a country-wide or market level
for a new system, then the traffic needs to be distributed in a weighted proportion
to each of the markets being designed for the system or homogeneously
distributed for a given market.
The forecasting for voice traffic is well documented and will only get a
superficial treatment here. However, the real issue with traffic dimensioning
lies in the ability to forecast both the circuit switched as well as the new
packet services that will be used by the customers of the wireless operator.
The ultimate question that the designer must answer is, “how do you
plan on supporting the traffic with their prescribed services?”
Because there are numerous types of services available for both circuit
switched as well as packet, some generalizations need to be made in
order to have a chance at arriving at some conclusions necessary for
input into the design phase. Therefore the symbols defined in Table 13-6
will be used to help define the different classifications of transport services
required.

For a new or existing system, the issue of where to begin is always the
hardest part. However, one of the key parameters you need to obtain from
marketing and/or sales is the penetration rate, take rate for each of the services types offered. This can be achieved via several methods, such as a
general approach where a standard percentage, percent, is used for say
packet services. Or you could base the amount of packet data subscribers
from the number of handsets expected to be purchased for resale in the
market.

Regardless, the first step in any traffic study is to determine the population
density for a given market; in the case of an existing system, the population
density and primary penetration rates are already built into the
system due to known loading issues. However, especially for new services,
like packet data, the process of determining the population density for a
given area followed by the multiplication of this by the penetration rate will
greatly help in the determination of the expected traffic load from which to
design the system. 501